Cu掺杂β-Si_(3)N_(4)的力学性能和电子结构的第一性原理研究

First-principles calculations of mechanical properties and electronic structures of Cu dopedβ-Si_(3)N_(4)

采用基于密度泛函的第一性原理方法研究了(Si_(3-x)Cu_(x))N_(4)(x=0,0.25,0.5,0.75,1)晶体的稳定性、力学性能和电子结构,分析了Cu掺杂对β-Si_(3)N_(4)力学性能的影响机制.结果表明,(Si_(3-x)Cu_(x))N_(4)为热力学稳定结构,Cu掺杂降低了β-Si_(3)N_(4)的稳定性.由弹性常数和Voigt-Reuss-Hill近似看出,(Si_(3-x)Cu_(x))N_(4)满足波恩力学稳定性判据,Cu掺杂使得β-Si_(3)N_(4)的体模量、剪切模量和杨氏模量降低,当x=0时,(Si_(3-x)Cu_(x))N_(4)的体模量、剪切模量和杨氏模量最大,分别为234.3 GPa、126.7 GPa和322.1 GPa.根据泊松比和G/B值判断出(Si_(3-x)Cu_(x))N_(4)属于韧性材料,Cu掺杂增强了β-Si_(3)N_(4)的韧性,(Si_(2)Cu)N_(4)的韧性最好.由能带结构、态密度、布局电子数和重叠布居数可知,Cu掺杂降低了β-Si_(3)N_(4)的共价键和离子键强度、提高了金属性,这是Cu掺杂降低β-Si_(3)N_(4)稳定性、增强其韧性的主要原因.

The stabilities,mechanical properties and electronic structures of(Si_(3-x)Cu_(x))N_(4)(x=0,0.25,0.5,0.75,1)crystals were studied by using the first-principles calculations based on the density functional theory(DFT).The results reveal that(Si_(3-x)Cu_(x))N_(4) has a thermodynamically stable structure,and the stability ofβ-Si3N4 is reduced by Cu doping.The calculated elastic constants and the Voigt-Reuss-Hill approximation indicate that the bulk modulus,shear modulus and Young’s modulus ofβ-Si_(3)N_(4) are reduced by Cu doping,and they reach the maximum values of respectively 234.3 GPa,126.7 GPa and 322.1 GPa when x=0.Based on Poisson’s ratio and G/B value,(Si_(3-x)Cu_(x))N_(4) is ductile material,the toughness ofβ-Si_(3)N_(4) increases with the increase of x and obtain the maximum result when x=1.The results of the band structure,density of states,charge distributions and overlapping populations reveal that Cu doping reduces the covalent bond and ionic bond strengths,enhances metallicity,reduces the structural stability ofβ-Si_(3)N_(4),and hence enhances the toughness ofβ-Si_(3)N_(4).The results of this study will provide theoretical and experimental guidance for improving the toughness ofβ-Si_(3)N_(4).